1. Field of the Invention
The present invention relates to an ink jet printer, and, more particularly, to an ink jet printer having a printhead with a continuous sealing surface for coupling to a moisture leakage resistant capping member.
2. Description of the Related Art
Ink jet printing systems can generally be divided into two types: one type which uses thermal energy to produce a vapor bubble in an ink filled channel that expels a droplet of ink; and a second type which uses a piezoelectric transducer to produce a pressure pulse that expels a droplet from a nozzle.
Thermal ink jet printing systems use thermal energy selectively produced by resistors located in capillary-filled ink channels near channel terminating nozzles or orifices to momentarily vaporize the ink and form bubbles on demand. Each temporary bubble expels an ink droplet and propels it towards a recording medium. The printing system may be incorporated in either a carriage-type printer or a pagewidth type printer. The carriage-type printer generally has a relatively small printhead containing the ink channels and nozzles. The printhead is usually sealingly attached to an ink manifold or to a disposable ink supply cartridge. The combined printhead and manifold or cartridge assembly is reciprocated to print one swath of information at a time on a stationarily held recording medium, such as paper. After the swath is printed, the paper is stepped a distance equal to the height of the printed swath, so that the next printed swath will be contiguous therewith. The procedure is repeated until the entire page is printed. In contrast, the pagewidth printer has a stationary printhead having a length equal to or greater than the width of the paper. The paper is continuously moved past the pagewidth printhead in a direction normal to the printhead length and at a constant speed during the printing process.
Piezoelectric activated ink jet printing systems use a pulse generator which provides an electric signal. The signal is applied across crystal plates, one of which contracts and the other of which expands, thereby causing the plate assembly to deflect toward a pressure chamber. This causes a decrease in volume which imparts sufficient kinetic energy to the ink in the printhead nozzle so that one ink droplet is ejected onto a recording medium.
In the ink jet printing systems of the above- types, several problems have arisen which adversely affect the quality of performance of printing. Among these problems are 1) evaporation of the volatile ink ingredients, including water; 2) clogging of the printhead nozzles caused by ink drying therein due to non-use for a period of time; 3) adherence of dust to the nozzle-containing face of the printhead due to the moisture of fluid ink around the nozzle; 4) leakage of ink from the nozzles; 5) bubbles and dust taken into the printhead nozzles as a result of external causes such as vibration imparted to the printhead and environmental changes occurring around the printhead; and 6) contamination of the printhead nozzles when the printhead is not in use, such contamination including, for example, non-collapsing air bubbles.
To alleviate these problems and enhance the quality and performance of the printhead, protective caps have been developed to cover the printhead when printing is not occurring. Generally, these caps are applied to a printhead when it is in its "home position" between printing jobs. However, a reliable seal is difficult to achieve with the capping members because the printhead assembly is often not fluid-tight or sufficiently vapor-tight. Also, if the surfaces surrounding the printhead die, such as the ink manifold and substrate, are not precisely aligned, there will be a discontinuous surface for the capping member to abut. Therefore, air leaks may occur between the printhead and the cap which allow the printhead die to become contaminated and cause the volatile ink ingredients to evaporate.
Several approaches have been proposed to address the above problems. For example, U.S. Pat. No. 4,390,883 to Stoneburner discloses a fluid jet printer within an inflation means for internally sealing the nozzles and their printhead. This approach internally blocks ink from passing through the nozzles but does not provide exterior protection.
Related U.S. Patent Application 07/542,053 now U.S. Pat. No. 5,065,170, to Rezanka et al. uses a capping member which abuts the printhead die. The die sits on a resilient gasket, but a continuous surface between the front surfaces of the substrate and manifold is not provided.
U.S. Pat. No. 4,914,562 to Abe et al., discloses a protective film which covers the heating elements within a thermal ink jet. However, this approach does not prevent evaporation or contamination of ink through the nozzles.
Another approach to protecting the heating elements of a thermal ink jet printer is shown by U.S. Pat. No. 4,777,494 to Shibata et al., which uses electrodes having a protective layer which is self-healing through anodic oxidation treatment. A method of sealing ink jet printhead components together using adhesive between upper and lower plates of a printhead die is shown by U.S. Pat. No. 4,678,529 to Drake et al. However, this approach does not seal the printhead die to the manifold or substrate.